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Sung-Won Lee

Study of Jets Production Association with a Z boson in pp Collision at 7 and 8 TeV with the CMS Detector. Kittikul Kovitanggoon Texas Tech University. Sung-Won Lee. 1. Angular Correlation of Z and a jet. '' Z+jet'' events are predominantly produced by quark exchange processes

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Sung-Won Lee

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  1. Study of Jets Production Association with a Z boson in pp Collision at 7 and 8 TeV with the CMS Detector Kittikul Kovitanggoon Texas Tech University Sung-Won Lee 1

  2. Angular Correlation of Z and a jet • ''Z+jet'' events are predominantly produced by quark exchange processes (i.e. qq̄ → Z 0 g and qg → Z 0 q as shown in the previous slide) • In the center-of-momentum frame (variables are marked with “ * ”), the differential cross section is The observed cosθ* distribution can be used to indicated a new particle or improved pQCD as feed back to experts We focus on angular variables which closely related to cosθ* • Rapidity distributions of Z boson: |yz| • Rapidity distributions of leading jet: |yjet| • Rapidity difference: ydiff = 0.5|yz-yjet| • Related to the scattering angle at the center of momentum frame: tanh(ydiff) = β*cosθ* • Rapidity average: ysum = 0.5|yz+yjet| • Rapidity boost from the center of momentum frame to the lab frame

  3. Combined Results (Electron + Muon) Phys. Rev. D 88, 112009 (2013) The data for the |yZ| and |yjet| distributions agree to better than 5% accuracy However, MADGRAPH (LO PDF) is less consistent with the data

  4. Combined Results (Electron + Muon) Phys. Rev. D 88, 112009 (2013) • The data agree with all predictions at low region • At high region, SHERPA is the better prediction than MEADGRAPH amd MCFM • LO PDF makes MADGRAPH less consistent with the data

  5. Combined Results (Electron + Muon) Phys. Rev. D 88, 112009 (2013) • The ydif distribution is consistent with MCFM for ydif < 1 • The two hybrid programs differ considerably in the prediction for ydif • The difference in the distribution of ydif can be attributed to the matching algorithm, with the SHERPA CKKW scheme appearing more consistent with the data • The difference in ydiff between the LO and NLO matrix elements is due to the contribution from NLO diagrams with a gluon propagator that yield more forward rapidities

  6. Z+jets differential Cross Section • Z+jets differential cross section measurements can be used to improve high order pQCD calculation • Z+jets can be the major background for new physics • Two of the Higgs decay modes are H → ZZ and ZH → l+l-bƀ • Search of dark matter in SUSY (gluino cascades) • This analysis is the update with 2012 at 8TeV • Ongoing analysis SMP-13-007 • The Z+jets production cross section as a function of the jet multiplicity : dσ/ dNJ • The Z+jets cross section as a function of the jet pT : dσ/ dpT • The Z+jets cross section as a function of the jet η : dσ/ dη

  7. Results Njet • The trend of the jet multiplicity represents the expectation of the pQCD prediction for an exponential decay with number of jets • MADGRAPH is a good description of data for jet multiplicity

  8. Results (II) pTjet 1st leading jet 2nd leading jet • MADGRAPH provides a globally satisfactory description of data,but slightly overestimating the first and second leading jet spectra at high pT

  9. Results (II) ηjet 1st leading jet 2nd leading jet • MADGRAPH shows the slightly overestimate in the |η|<0.6 and underestimate in the |η|>1.6

  10. Conclusions • Jets productions in association with a Z boson in p-p collision provides a good opportunity to test perturbative QCD and important background for new physics • Angular distributions for the Z boson and a single jet of 5.0 fb− 1 at 7 TeV have been analyzed • Differential cross sections for the Z boson and jets of 19.8 fb− 1 at 8 TeV have been calculated • More detail studies for Differential cross sections (i.e. complete uncertainty and combine results with electron channel) will be done

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